At a Glance

Why Get Tested?

To diagnose dengue fever, particularly if you are experiencing fever after travel to a tropical or subtropical destination

When to Get Tested?

When you develop a high fever within 2 weeks of travel to an area where dengue fever is endemic or an outbreak is occurring

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Dengue fever is a viral infection transmitted to humans by mosquitoes that live in tropical and subtropical climates and carry the virus. Blood testing detects the dengue virus or antibodies produced in response to dengue infection.

If a person develops a fever within two weeks following travel to an area where dengue fever is present, it may be prudent to test for dengue fever. According to the Centers for Disease Control and Prevention (CDC), dengue infections have been reported in more than 100 countries from parts of Africa, the Americas, the Caribbean, the Eastern Mediterranean, Southeast Asia, and the Western Pacific. It is a fast emerging infectious disease, according to the World Health Organization (WHO), with an increasing number of cases and countries affected throughout the world. Approximately 50 to 100 million cases occur annually worldwide.

In the U.S., the majority of dengue cases occur in travelers returning from areas where dengue is endemic. Most dengue cases in U.S. citizens occur in those inhabitants of Puerto Rico, the U.S. Virgin Islands, Samoa and Guam. Outbreaks where a large number of cases occur in a defined area are rare in the U.S. In recent years, there have been small outbreaks in Texas and Hawaii and a few cases diagnosed in southern Florida.

Many individuals will develop no symptoms at all, or have only a mild illness when exposed to one of the four serotypes of the dengue virus. For those who do develop symptoms, prognosis is still very good for full recovery within a few weeks. The most common initial symptoms are a sudden high fever (104°F or 40°C) and flu-like symptoms that appear roughly 4 to 7 days after being bitten by an infected mosquito (this is called the incubation period and can range from 3 to 14 days). Additional signs and symptoms may include severe headache, especially behind the eyes, muscle and joint pain, skin rash, nausea, vomiting, and swollen glands.

Some people who develop a fever will recover on their own with no lasting ill effects while others may progress to severe dengue fever (sometimes called Dengue Hemorrhagic Fever). If the disease progresses to this form, a new wave of symptoms will appear 3 to 7 days after initial symptoms and as the fever recedes. These may include nose bleeds, vomiting blood, passing blood in the stool, difficulty breathing and cold clammy skin, especially in the extremities. During the second phase, the virus may attack blood vessels (the vascular system), causing capillaries to leak fluid into the space around the lungs (pleural effusion) or into the abdominal cavity (ascites). Currently, there is no explanation as to why dengue fever resolves itself harmlessly in some people while progressing to the severe form in others.

The loss of blood and fluid during the second phase, if untreated, can sometimes develop into a rare condition known as Dengue Shock Syndrome and can be fatal. In order to avoid that complication, a doctor may hospitalize a patient with dengue fever so that falling blood pressure and dehydration caused by the loss of blood and fluids can be managed while the disease runs its course – generally a period of one to two weeks. During the following week of recovery, a person may develop a second rash that lasts a week or more.

Dengue fever is usually diagnosed via some combination of blood tests because the body's immune response to the virus is dynamic and complex. Laboratory tests may include:

Molecular tests for dengue virus (PCR)—detect the presence of the virus itself; these tests can diagnose dengue fever up to 5 days after the onset of symptoms.

Antibody tests, IgM and IgG—detect antibodies produced by the immune system when a person has been exposed to the virus; these tests are most effective when performed at least 7-10 days after exposure.

Complete blood count (CBC)—to look for low platelet count typical of the later stages of the illness and to detect the decrease in hemoglobin, hematocrit, and red blood cell (RBC) count (evidence of anemia) that would occur with blood loss associated with severe dengue fever

Is any test preparation needed to ensure the quality of the sample?

The Test

How is it used?

Dengue fever testing is used to determine whether a person with symptoms and recent potential exposure to dengue has been infected. The infection is difficult to diagnose without laboratory tests because symptoms may initially resemble other diseases, such as malaria. Two types of testing are available:

Antibody tests—these tests are primarily used to help diagnose a current or recent infection. They detect two different classes of antibodies produced by the body in response to a dengue fever infection, IgG and IgM. Diagnosis may require a combination of these tests because the body's immune system produces varying levels of antibodies over the course of the illness. IgM antibodies are produced first and tests for these are most effective when performed at least 7-10 days after exposure. Levels in the blood rise for a few weeks, then gradually decrease. After a few months, IgM antibodies fall below detectable levels. IgG antibodies are produced more slowly in response to an infection. Typically, the level rises with an acute infection, stabilizes, and then persists long-term. Individuals who have been exposed to the virus prior to the current infection maintain a level of IgG antibodies in the blood that can affect the interpretation of diagnostic results.

Molecular testing (polymerase chain reaction, PCR)—this type of test detects the genetic material of the dengue virus in blood up to 5 days after symptom onset (fever).

Testing is usually ordered within one to two weeks of the onset of symptoms to detect an acute infection. If antibody testing is performed, an additional blood sample may be collected after two weeks of symptoms to determine if the antibody level is rising.

What does the test result mean?

Antibody testing—antibody tests may be reported as positive or negative, or may be reported as an antibody titer with an interpretation of which type(s) of antibody (IgG or IgM) is present.

Positive IgM and IgG tests for dengue antibodies detected in an initial blood sample mean that it is likely that the person became infected with dengue virus within recent weeks. If the IgG is positive but the IgM is low or negative, then it is likely that the person had an infection sometime in the past. If the dengue IgG antibody titer increases four-fold or greater (e.g., titer of 1:4 to a titer of 1:64) between an initial sample and one taken 2 to 4 weeks later, then it is likely that a person has had a recent infection.

Negative tests for IgM and/or IgG antibodies may mean that the individual tested does not have a dengue infection and symptoms are due to another cause, or that the level of antibody may be too low to measure. The person may still have a dengue infection – it may just be that it is too soon after initial exposure to the virus to produce a detectable level of antibody.

The following table summarizes results that may be seen with antibody testing:

IgM Result

IgG Result

Possible Interpretation

Positive

Negative

Current infection

Positive

Positive

Current infection

Low or negative or not tested

Four-fold increase in samples taken 2-4 weeks apart

Recent infection

Low or negative

Positive

Past infection

Negative

Negative

Too soon after initial exposure for antibodies to develop or symptoms due to another cause

Molecular testing—a PCR test that detects the presence of the virus itself is generally considered the most reliable means of diagnosis, but the test is not widely available. A positive result from a PCR is considered conclusive. A negative result on a PCR test may indicate that no infection is present or that the level of virus is too low to detect, as may happen if the test was performed after the 5-day window during which the virus is present in the sample collected for this test. If very recent exposure is suspected, repeating the test at a later time may be warranted.

Is there anything else I should know?

Physical symptoms like rash or aching joints are not a reliable means for diagnosing dengue fever because the symptoms are not likely to appear until after the initial fever has passed.

Antibody tests for dengue fever can be positive if a person is infected with another arbovirus such as West Nile virus. A health practitioner will consider a person's test results, medical history, and recent travel history in making a diagnosis.

No laboratory test can predict whether or not the infection will progress to the more severe form.

Common Questions

1. Can dengue fever be prevented?

Currently, there is no immunization that will prevent a person from contracting dengue fever if exposed to the virus. Limiting exposure to the virus depends upon protecting against mosquito bites. When traveling in tropical climates, wear insect repellent that contains DEET and long sleeved-shirts and long pants. Stay indoors during dawn and dusk when mosquitoes are most active.

2. Can dengue fever be passed from person to person?

No, the virus is not spread by person-to-person contact or by exposure to respiratory secretions. The virus is spread when a mosquito bites an infected person, then bites a healthy person. It may be transmitted in rare cases through a blood transfusion, organ donation, or mother to fetus.

3. If I have had dengue fever, can I get it again?

Yes. There are four serotypes of the dengue virus. There is no cross-protective immunity to all dengue viruses when you are exposed to one serotype. In addition, a subsequent infection with a dengue fever virus is usually associated with more severe disease.

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Article Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

De Paula, S. and Fonseca, B. (2004). Dengue: a review of the laboratory tests a clinician must know to achieve a correct diagnosis. The Brazilian Journal of Infectious Diseases: an Official Publication of the Brazilian Society of Infectious Diseases. Available online at http://europepmc.org/abstract/MED/15880229 through http://europepmc.org. Accessed June 2013.

Rathakrishnan, A., Sekaran, S. (2013). New development in the diagnosis of dengue infections. Expert Opinion on Medical Diagnostics. Available online at http://www.ncbi.nlm.nih.gov/pubmed/23530846 through http://www.ncbi.nlm.nih.gov/pubmed. Accessed 6/1/2013.

(January 23, 2013) National Institute of Allergy and Infectious Diseases. Dengue Fever. Available online at http://www.niaid.nih.gov/topics/denguefever/Pages/default.aspx through http://www.niaid.nih.gov. Accessed June 2013.

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This article was last reviewed on July 24, 2013. | This article was last modified on February 24, 2015.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.